It is known that ventilators or fans coupled to electric machinery emit a substantial amount of noise. This is so particularly for three-phase alternators for vehicular use. It has been proposed to dampen the noise level of a ventilator or fan of a three-phase alternator by a rubber bearing - see the reference in German Patent Disclosure Document No. DE-OS 28 39 288, assigned to the Assignee of the present application.
In this known bearing, the elastomer or rubber forms a direct bearing means. In other words, the ventilator or fan is supported via an intermediate rubber part; with a generally rigid fastening, for example, either a rubber gasket is fastened in between, or rubber separators are located on both sides in the radial or axial direction, as part of the fan bearing itself, for example. Bearing a fan directly in this way via an interposed, optionally annular rubber element enables a shift in the resonance of the fan, thus damping noise development at selected speed ranges. Tests have shown that the noise emitted by fans and ventilators correlates closely with the resonant frequencies, such as torsion vibration and the like, of the rotor structure of the generator involved.